Embodiments of the present invention are directed to pumps, pumping systems, valves used to operate such pumps and pumping systems and methods of using such pumps and pumping systems. The pumps and pumping systems of the present invention have particular utility in applications in which a constant flow is desired.
Chromatography is the separation of mixtures of compounds in solution as the solution passes through or over an immobile non-miscible or stationary phase. The compounds of the mixture separate as a result of the individual and different affinity each compound has for the stationary or immiscible phase. The compound held in solution is referred to as the analyte. The material in which the compound is dissolved is known as the solute.
High performance liquid chromatography (HPLC) processes use one or more pumps to propel a liquid solution through a stationary phase. Gas chromatography methods use pressurized or pumped gases to propel a gas solution through or against a stationary phase. Super-critical gas chromatography employs gases at temperatures and pressures such the gases have liquid-like salvation properties and gas like permeability properties.
Many chromatographic processes employ a stationary phase of packed particles or a porous monolithic material, contained in a column or cartridge, through which a solution is passed. Capillary chromatography uses a fine tube, or capillary, either packed with particles, or using the walls of the capillary, to effect separations.
Chromatography pumps normally operate at pressures of up to 5,000 to 6000 psi and, even more preferably, up to 15,000 psi. Compounds are frequently identified by a characteristic time of retention. The retention time is the period of time in which the material is retained in the stationary phase after entering. Compounds elute or leave the stationary phase either due to time or change in the composition of the fluids flowing through the stationary phase. It is common to change the composition of the solution over time to release compounds from the stationary phase.
Some of the solutions routinely used in performing chromatography are difficult to pump precisely due to the change of volume of the liquid as it is compressed and undergoes changes in temperature. Some of the solutions are corrosive, leave residue, dissolve mechanical parts of the pump, or become gaseous when subjected to changes in pressure.
It is desirable to pump the liquids and gases used in chromatographic process at a constant flow rate. However, if the composition of the solution is changing over time, the difficult task of maintaining constant flow to a column, cartridge or capillary becomes even more complex.
Thus, there is a need for pumps that can propel fluids with precise control of the flow rate, with few pressure perturbations and with a minimum of moving mechanical parts in contact with fluids.